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Spacecraft wakes in the solar wind

Anders I. Eriksson, Yuri Khotyaintsev, Per-Arne Lindqvist

Abstract

The solar wind flow creates a wake behind any spacecraft immersed in it. We study the properties of this wake using the spherical electrostatic probes of the Electric Fields and Waves (EFW) instruments on the Cluster satellites. The satellites spin in a plane inclined only a few degrees with respect to the ecliptic plane. The solar wind is often close to this plane, so each probe (44 m away from the spin axis) passes through the wake once every spin period (around 4 s), thereby sampling a cut of the wake electrostatic potential structure. The signature of the wake is clearly seen in the data as a pulse with an amplitude typically of a few tenths of a volt. We present statistics of the wake signatures as well as detailed examples, compare to solar wind parameters, and show a method to remove the wake signature from the electric field measurements.

Spacecraft wakes in the solar wind

Abstract

The solar wind flow creates a wake behind any spacecraft immersed in it. We study the properties of this wake using the spherical electrostatic probes of the Electric Fields and Waves (EFW) instruments on the Cluster satellites. The satellites spin in a plane inclined only a few degrees with respect to the ecliptic plane. The solar wind is often close to this plane, so each probe (44 m away from the spin axis) passes through the wake once every spin period (around 4 s), thereby sampling a cut of the wake electrostatic potential structure. The signature of the wake is clearly seen in the data as a pulse with an amplitude typically of a few tenths of a volt. We present statistics of the wake signatures as well as detailed examples, compare to solar wind parameters, and show a method to remove the wake signature from the electric field measurements.
Paper Structure (9 sections, 5 equations, 8 figures)

This paper contains 9 sections, 5 equations, 8 figures.

Table of Contents

  1. INTRODUCTION
  2. EXAMPLE DATA
  3. WAKE IDENTIFICATION AND REMOVAL
  4. WAKE STATISTICS
  5. 1D distributions
  6. Gaussian wake modelling
  7. 2D distributions
  8. NUMERICAL SIMULATION WITH SPIS
  9. CONCLUSIONS

Figures (8)

  • Figure 1: Sketch of Cluster and EFW probe geometry, with the wake forming behind the spacecraft. In reality, the wake will spread out at an angle related to the flow Mach number.
  • Figure 2: Example of solar wind wake signature in Cluster EFW data. The blue curve is the original raw data, while the green curve shows the data after wake removal (Section \ref{['sec:fix']}). The red stars, bound together by the red curve, shows the wake amplitude determined in the removal process, once for each spacecraft spin period.
  • Figure 3: An example of wake identification and removal from one spin of EFW data from Cluster 3. (a) The electric field data for the spin under study are plotted in black, with the four adjacent spins given in green. (b) The second derivative of the weighted average of the five spin periods of data above. (c) After smoothing of the second derivative, it is integrated twice to give a wake time series. This is set to zero far from the wake centre. The amplitude and width of the wake are determined from these data. (d) The original time seried (blue) and the corrected data (green).
  • Figure 4: Full resolution raw (blue) and wake corrected (green) electric field data from EFW probes 1 and 2 on Cluster 3. The red curve denotes the wake amplitude. The lower panel is a zoom in to a detail of the upper panel.
  • Figure 5: Statistical distributions of wake parameters and related data for the statistical sample used in this paper. On top of each panel is given the mean $m$, standard deviation $s$ and normalized spread $s/m$ for the plotted variable.
  • ...and 3 more figures